class Person{
  String name='';
  int age=0;
  final String gender;
  Person(String name,int age,String gender):gender=gender{
    this.name=name;
    this.age=age;
  }
  Person.withName(this.name,this.gender);
  Person.withAge(this.age,this.gender);
}

class World{
  final num size;
  final String name;
  const World(this.size,this.name);
}

class Logger{
  final String name;
  Logger._internal(this.name);
  factory Logger(String name){
    return Logger._internal('Dart');
  }
}

void main(){
  var person = new Person('Tom',20,'Male');
  var person2 = new Person.withName('John','Male');
  var person3 = new Person.withAge(17,'Female');
  const world = World(100,'Earth');
  var log = Logger('record');
}
